Moulded bodies consisting of core-shell particles

ABSTRACT

The invention relates to mouldings having an optical effect which essentially consist of core/shell particles whose shell forms a matrix and whose core is essentially solid and has an essentially monodisperse size distribution, where a difference exists between the refractive indices of the core material and of the shell material. The mouldings are characterised in that they are obtainable by a process in which the core/shell particles are heated to a temperature at which the shell is flowable, and the flowable core/shell particles are subjected to the action of a mechanical force.

[0001] The invention relates to mouldings having an optical effect whichessentially consist of core/shell particles, to the core/shellparticles, and to processes for the production of the mouldings orcore/shell particles.

[0002] Polymeric core/shell particles have been recommended for theproduction of adhesives, binder systems, in particular also asreinforcing materials in the production of certain groups of compositematerials. Composite materials of this type consist of a plastic matrixand reinforcing elements embedded therein. One problem in the productionof materials of this type consists in the production of a positiveconnection between the matrix material and reinforcing material. Only ifsuch a connection exists can forces be transferred from the matrix tothe reinforcing elements. The more the mechanical properties of thematrix material and reinforcing material, in particular with respect toelasticity, hardness and deformability, differ from one another, thegreater the risk of detachment of the matrix from the reinforcingelements. This risk is countered by coating the polymeric reinforcingparticles with a second polymer material which is more similar to thematrix material and is therefore able to form a stronger bond to thematrix (Young-Sam Kim, “Synthesis and Characterisation of MultiphasePolymeric. Lattices Having a Core/Shell Morphology”, dissertation,University of Karlsruhe (TH), Shaker Verlag, Aachen (1993), pages 2-22).In addition, it has also been recommended to graft the coating polymeronto the reinforcing polymer in order also to prevent detachment of theshell from the reinforcing particles by means of covalent bonds (W.-M.Billig-Peters, “Core/Shell Polymers with the Aid of Polymeric AzoInitiators”, dissertation, University of Bayreuth (1991).

[0003] The specific production of core/shell polymers is generallycarried out by stepwise emulsion polymerisation, in which firstly alatex of core particles is produced in the first step, and the shellpolymer is produced in the second step. In this process, the coreparticles act as “seed particles”, onto the surface of which the shellpolymers are preferably deposited.

[0004] The deposition may result in a more or less symmetrical shellaround core particles, but it is also possible for irregular depositionsto take place, giving structures having a blackberry-like appearance. Agood review of the production of two-phase polymer particles and thephenomena which occur in the process, in particular the formation ofcore/shell particles, is given in the dissertation by KatharinaLandfester, “Synthesis and Characterisation of Core/Shell Lattices UsingElectron Microscopy and Solid-State NMR”, University of Mainz (1995).

[0005] Natural precious opals are built up from domains consisting ofmonodisperse, closely packed and therefore regularly arranged silica gelspheres having diameters of 150-400 nm. The colour play of these opalsis created by Bragg-like scattering of the incident light at the latticeplanes of the domains arranged in a crystal-like manner.

[0006] There has been no lack of attempts to synthesise white and blackopals for jewellery purposes using water-glass or silicone esters asstarting material.

[0007] U.S. Pat. No. 4,703,020 describes a process for the production ofa decorative material consisting of amorphous silica spheres which arearranged in a three-dimensional manner, with zirconium oxide orzirconium hydroxide being located in the interspaces between thespheres. The spheres have a diameter of 150-400 nm. The production iscarried out in two steps. In a first step, silicon dioxide spheres areallowed to sediment from an aqueous suspension. The resultant materialis then dried in air and subsequently calcined at 800° C. In a secondstep, the calcined material is introduced into the solution of azirconium alkoxide, the alkoxide penetrating into the interspacesbetween the cores, and zirconium oxide being precipitated by hydrolysis.This material is subsequently calcined at 1000-1300° C.

[0008] U.S. Pat. No. 4,434,010 discloses inorganic-based pigments whichhave a highly pronounced colour flop. These pigments are characterisedby an extremely homogeneous structure comprising layers having differentrefractive indices. This structure results in pronounced interferenceeffects, which are utilised for the generation of colour. However, theproduction of these pigments is difficult and only possible by means ofcomplex and expensive production processes.

[0009] U.S. Pat. No. 5,364,557 discloses organic effect pigments basedon cholesteric liquids. In these pigments, an interference effect arisesdue to a helical superstructure. Here too, the materials necessary forthe production are complicated to produce and therefore very expensive.The pigments are produced from the cholesteric liquid crystals (LCs) byapplying the cholesteric material in a thin layer to a support foil,carrying out a photochemical polymerisation in the LC phase, anddetaching the resultant film from the foil and grinding it. Besides theexpensive production of the starting materials, a severe disadvantage ofthis process is that extremely great attention must be paid to alignmentof the LCs during the production process since this can be adverselyaffected by even extremely small amounts of impurities.

[0010] A process for the coating and printing of substrates in whichcholesteric liquid crystals are used is disclosed in WO 96/02597. Inthis process, one or more liquid-crystalline compounds, at least one ofwhich is chiral, and which contain one or two polymerisable groups, areapplied to a substrate together with suitable comonomers—if this iscarried out by a printing process, dispersants are also added to themixture—and copolymerised. The resultant layers can, if they arebrittle, be detached from the substrate, comminuted and used aspigments.

[0011] Furthermore, aqueous, monodisperse polymer dispersions are known,for example from T. Okubu, Prog. Polym. Sci. 18 (1993) 481-517, which,in liquid form, if necessary after post-purification, tend toward latexcrystallisation and thus result in colour effects.

[0012] A multiplicity of publications on the production of monodisperseparticles is known, for example EP-A-0 639 590 (production byprecipitation polymerisation), A. Rudin, J. Polym. Sci., 33 (1995)1849-1857 (monodisperse particles having a core/shell structure) andEP-A-0 292 261 (production with addition of seed particles).

[0013] EP-A-0 441 559 describes core/shell polymers having differentrefractive indices of core and shell and the use of these materials asadditives for paper-coating compositions.

[0014] EP-A-0 955 323 describes core/shell particles whose core andshell materials are able to form a two-phase system and which arecharacterised in that the shell material is filmable and the cores areessentially dimensionally stable under the conditions of film formationof the shell, are only swellable by the shell material to a very smallextent, or not at all, and have a monodisperse size distribution, with adifference between the refractive indices of the core material and ofthe shell material of at least 0.001. The production of the core/shellparticles and their use for the production of effect colorants are alsodescribed. The process for the production of an effect colorantcomprises the following steps:

[0015] Application of the core/shell particles to a substrate of lowadhesive capacity, if necessary evaporation or expulsion of any solventor diluent present in the applied layer, transfer of the shell materialof the core/shell particles into a liquid, soft or visco-elastic matrixphase, orientation of the cores of the core/shell particles at least toform domains having a regular structure, curing of the shell material inorder to fix the regular core structure, detachment of the cured filmfrom the substrate, and, if a pigment or powder is to be produced,comminution of the detached film to the desired particle size. In thesecore/shell particles disclosed in EP-A-0 955 323, the core “floats” inthe shell matrix; a long-range order of the cores does not form in themelt, merely a close-range order of the cores in domains. Theseparticles are thus of only restricted suitability for processing by theusual methods for polymers.

[0016] For industrial applications, however, it would be desirable to beable to produce even large-area structures or three-dimensionalmouldings directly with a long-range order of the cores, with thestructures or mouldings exhibiting the optical effect homogeneously andvery brightly over the entire area.

[0017] The object of the present invention was to avoid theabove-mentioned disadvantages and to provide mouldings which can beobtained using conventional processing methods.

[0018] The present invention therefore relates firstly to mouldingshaving an optical effect, essentially consisting of core/shell particleswhose shell forms a matrix and whose core is essentially solid and hasan essentially monodisperse size distribution, where a difference existsbetween the refractive indices of the core material and of the shellmaterial, characterised in that the mouldings are obtainable by aprocess in which a) the core/shell particles are heated to a temperatureat which the shell is flowable, and b) the flowable core/shell particlesare subjected to the action of a mechanical force.

[0019] The present invention furthermore relates to a process for theproduction of mouldings having an optical effect which is characterisedin that a) core/shell particles whose shell forms a matrix and whosecore is essentially solid and has an essentially monodisperse sizedistribution, where a difference exists between the refractive indicesof the core material and of the shell material, are heated to atemperature at which the shell is flowable, and b) the flowablecore/shell particles from a) are subjected to a mechanical force.

[0020] For the purposes of the present invention, the term opticaleffect is taken to mean both effects in the visible wavelength region oflight and, for example, effects in the UV or infrared region. It hasrecently become established practice to refer to such effects in generalas photonic effects. All these effects are optical effects for thepurposes of the present invention, with the effect, in a preferredembodiment, being opalescence in the visible region. In a conventionaldefinition of the term, the mouldings according to the invention arephotonic crystals (cf. Nachrichten aus der Chemie; 49(9), September2001; pp. 1018-1025).

[0021] It is particularly preferred for the purposes of the presentinvention for the shell in the core/shell particles to be bonded to thecore via an interlayer.

[0022] It is furthermore preferred for the purposes of the presentinvention for the core of the core/shell particles to consist of amaterial which is either not flowable or becomes flowable at atemperature above the melting point of the shell material. This can beachieved through the use of polymeric materials having a correspondinglyhigh glass transition temperature (T_(g)), preferably crosslinkedpolymers, or through the use of inorganic core materials.

[0023] The suitable materials are described below in detail.

[0024] In a preferred variant of the production of mouldings accordingto the invention, the temperature in step a) is at least 40° C.,preferably at least 60° C., above the glass transition temperature ofthe shell of the core/shell particles. It has been found empiricallythat the flowability of the shell in this temperature range meets therequirements for economical production of the mouldings to a particularextent.

[0025] In a likewise preferred process variant which results in themouldings according to the invention, the flowable core/shell particlesare cooled under the action of the mechanical force from b) to atemperature at which the shell is no longer flowable.

[0026] For the purposes of the present invention, the action ofmechanical force can be the action of a force which occurs in theconventional processing steps of polymers. In preferred variants of thepresent invention, the action of mechanical force takes place either:

[0027] through uniaxial pressing or

[0028] action of force during an injection-moulding operation or

[0029] during a transfer moulding operation,

[0030] during (co)extrusion or

[0031] during a calendering operation or

[0032] during a blowing operation.

[0033] If the action of force takes place through uniaxial pressing, themouldings according to the invention are preferably films. Filmsaccording to the invention can preferably also be produced bycalendering, film blowing or flat-film extrusion. The various ways ofprocessing polymers under the action of mechanical forces are well knownto the person skilled in the art and are revealed, for example, by thestandard textbook Adolf Franck, “Kunststoff-Kompendium” [PlasticsCompendium]; Vogel-Verlag; 1996.

[0034] If mouldings are produced by injection moulding, it isparticularly preferred for the demoulding not to take place until afterthe mould with moulding inside has cooled. When carried out in industry,it is advantageous to employ moulds having a large cooling-channel crosssection since the cooling can then take place in a relatively shorttime. It has been found that cooling in the mould makes the coloureffects according to the invention much more intense. It is assumed thatbetter disordering of the core/shell particles to form the latticeoccurs in this uniform cooling operation. It is particularlyadvantageous here for the mould to have been heated before the injectionoperation.

[0035] The mouldings according to the invention may, if it istechnically advantageous, comprise auxiliaries and additives here. Theycan serve for optimum setting of the applicational data or propertiesdesired or necessary for application and processing. Examples ofauxiliaries and/or additives of this type are antioxidants, UVstabilisers, biocides, plasticisers, film-formation auxiliaries,flow-control agents, fillers, melting assistants, adhesives, releaseagents, application auxiliaries, demoulding auxiliaries and viscositymodifiers, for example thickeners.

[0036] Particularly recommended are additions of film-formationauxiliaries and film modifiers based on compounds of the general formulaHO—C_(n)H_(2n)—O—(C_(n)H_(2n)—O)_(m)H, in which n is a number from 2 to4, preferably 2 or 3, and m is a number from 0 to 500. The number n canvary within the chain, and the various chain members can be incorporatedin a random or blockwise distribution. Examples of auxiliaries of thistype are ethylene glycol, propylene glycol, di-, tri- and tetraethyleneglycol, di-, tri- and tetrapropylene glycol, polyethylene oxides,polypropylene oxide and ethylene oxide-propylene oxide copolymers havingmolecular weights of up to about 15,000 and a random or block-likedistribution of the ethylene oxide and propylene oxide units.

[0037] If desired, organic or inorganic solvents, dispersion media ordiluents, which, for example, extend the open time of the formulation,i.e. the time available for its application to substrates, waxes orhot-melt adhesives are also possible as additives.

[0038] If desired, UV and weathering stabilisers can also be added tothe mouldings. Suitable for this purpose are, for example, derivativesof 2,4-dihydroxybenzophenone, derivatives of 2-cyano-3,3′-diphenylacrylate, derivatives of 2,2′,4,4′-tetrahydroxybenzophenone, derivativesof o-hydroxyphenylbenzotriazole, salicylic acid esters,o-hydroxyphenyl-s-triazines or sterically hindered amines. Thesesubstances may likewise be employed individually or in the form of amixture.

[0039] The total amount of auxiliaries and/or additives is up to 40% byweight, preferably up to 20% by weight, particularly preferably up to 5%by weight, of the weight of the mouldings. Accordingly, the mouldingsconsist of at least 60% by weight, preferably at least 80% by weight andparticularly preferably at least 95% by weight, of core/shell particles.

[0040] In order to achieve the optical or photonic effect according tothe invention, it is desirable for the core/shell particles to have amean particle diameter in the range from about 5 nm to about 2000 nm. Itmay be particularly preferred here for the core/shell particles to havea mean particle diameter in the range from about 5 to 20 nm, preferablyfrom 5 to 10 nm. In this case, the cores may be known as “quantum dots”;they exhibit the corresponding effects known from the literature. Inorder to achieve colour effects in the region of visible light, it isparticularly advantageous for the core/shell particles to have a meanparticle diameter in the region of about 50-500 nm. Particularpreference is given to the use of particles in the range 100-500 nmsince in particles in this size range (depending on the refractive-indexcontrast which can be achieved in the photonic structure), thereflections of various wavelengths of visible light differ significantlyfrom one another, and thus the opalescence which is particularlyimportant for optical effects in the visible region occurs to aparticularly pronounced extent in a very wide variety of colours.However, it is also preferred in a variant of the present invention toemploy multiples of this preferred particle size, which then result inreflections corresponding to the higher orders and thus in a broadcolour play.

[0041] A further crucial factor for the intensity of the observedeffects is the difference between the refractive indices of core andshell. Mouldings according to the invention preferably have a differencebetween the refractive indices of the core material and of the shellmaterial of at least 0.001, preferably at least 0.01 and particularlypreferably at least 0.1.

[0042] In a particular embodiment of the invention, furthernanoparticles are included in the matrix phase of the mouldings inaddition to the cores of the core/shell particles. These particles areselected with respect to their particle size in such a way that they fitinto the cavities of the sphere packing of the cores and thus cause onlylittle change in the arrangement of the cores. Through specificselection of corresponding materials and/or the particle size, it isfirstly possible to modify the optical effects of the mouldings, forexample to increase their intensity. Secondly, it is possible throughincorporation of suitable “quantum dots”, to functionalise the matrixcorrespondingly. Preferred materials are inorganic nanoparticles, inparticular nanoparticles of metals or of II-VI or III-V semiconductorsor of materials which influence the magnetic/electrical (electronic)properties of the materials. Examples of preferred nanoparticles arenoble metals, such as silver, gold and platinum, semiconductors orinsulators, such as zinc chalcogenides and cadmium chalcogenides,oxides, such as haematite, magnetite or perovskite, or metal pnictides,for example gallium nitride, or mixed phases of these materials.

[0043] The precise mechanism which results in the uniform orientation(FIGS. 1 and 2) of the core/shell particles in the mouldings accordingto the invention was hitherto unknown. However, it has been found thatthe action of force is essential for the formation of the far-reachingorder. As shown in FIG. 3, it is assumed that the elasticity of theshell material under the processing conditions is crucial for theordering process. The chain ends of the shell polymers generally attemptto adopt a coiled shape. If two particles come too close, the coils arecompressed in accordance with the model concept, and repellent forcesarise. Since the shell-polymer chains of different particles alsointeract with one another, the polymer chains are stretched inaccordance with the model if two particles move away from one another.Due to the attempts by the shell-polymer chains to re-adopt a coiledshape, a force arises which pulls the particles closer together again.In accordance with the model concept, the far-reaching order of theparticles in the moulding (FIGS. 1 and 2) is caused by the interactionof these forces.

[0044] Particularly suitable core/shell particles for the production ofmouldings according to the invention have proven to be those whose shellis bonded to the core via an interlayer.

[0045] Core/shell particles whose core is essentially solid and has anessentially monodisperse size distribution, where a difference existsbetween the refractive index of the core material and that of the shellmaterial, and whose core consists of a material which is either notflowable or becomes flowable at a temperature above the melting point ofthe shell material and whose shell is bonded to the core via aninterlayer, and the use of such particles for the production ofmouldings are therefore further subject-matters of the presentinvention.

[0046] In a preferred embodiment of the invention, the interlayer is alayer of crosslinked or at least partially crosslinked polymers. Thecrosslinking of the interlayer here can take place via free radicals,for example induced by UV irradiation, or preferably via di- oroligofunctional monomers. Preferred interlayers in this embodimentcomprise from 0.01 to 100% by weight, particularly preferably from. 0.25to 10% by weight, of di- or oligofunctional monomers. Preferred di- oroligofunctional monomers are, in particular, isoprene and allylmethacrylate (ALMA). Such an interlayer of crosslinked or at leastpartially crosslinked polymers preferably has a thickness in the rangefrom 10 to 20 nm. If the interlayer comes out thicker, the refractiveindex of the layer is selected so that it corresponds either to therefractive index of the core or to the refractive index of the shell.

[0047] If copolymers which, as described above, contain a crosslinkablemonomer are employed as interlayer, the person skilled in the art willhave absolutely no problems in suitably selecting correspondingcopolymerisable monomers. For example, corresponding copolymerisablemonomers can be selected from a so-called Q-e-scheme (cf. textbooks onmacromolecular chemistry). Thus, monomers such as methyl methacrylateand methyl acrylate can preferably be polymerised with ALMA.

[0048] In another, likewise preferred embodiment of the presentinvention, the shell polymers are grafted directly onto the core via acorresponding functionalisation of the core. The surfacefunctionalisation of the core here forms the interlayer according to theinvention. The type of surface functionalisation here dependsprincipally on the material of the core. Silicon dioxide surfaces can,for example, be suitably modified with silanes carrying correspondinglyreactive end groups, such as epoxy functions or free double bonds. Othersurface functionalisations, for example for metal acides, can betitanates or organoaluminium compounds, each containing organic sidechains with corresponding functions. In the case of polymeric cores, thesurface modification can be carried out, for example, using a styrenewhich is functionalised on the aromatic ring, such as bromostyrene. Thisfunctionalisation then allows growing-on of the shell polymers to beachieved. In particular, the interlayer can also effect adhesion of theshell to the core via ionic interactions or complex bonds.

[0049] In a preferred embodiment, the shell of these core/shellparticles essentially consists of uncrosslinked organic polymers, whichare preferably grafted onto the core via an at least partiallycrosslinked interlayer.

[0050] The shell here can consist either of thermoplastic or elastomericpolymers. Since the shell essentially determines the material propertiesand processing conditions of the core/shell particles, the personskilled in the art will select the shell material in accordance with theusual considerations in polymer technology. In particular if movementsor stresses in a material are to result in optical effects, the use ofelastomers as shell material is preferred. In mouldings according to theinvention, the separations between the cores are changed by suchmovements. The wavelengths of the interacting light and the effects tobe observed change correspondingly.

[0051] The core can consist of a very wide variety of materials. Theessential factor according to the invention is, as already stated, thata refractive-index difference to the shell exists and the core remainssolid under the processing conditions.

[0052] It is furthermore particularly preferred in a variant of theinvention for the core to consist of an organic polymer, which ispreferably crosslinked.

[0053] In another, likewise preferred variant of the invention, the coreconsists of an inorganic material, preferably a metal or semimetal or ametal chalcogenide or metal pnictide. For the purposes of the presentinvention, chalcogenides are taken to mean compounds in which an elementfrom group 16 of the Periodic Table of the Elements is theelectronegative bonding partner; pnictides are taken to mean those inwhich an element from group 15 of the Periodic Table of the Elements isthe electronegative bonding partner.

[0054] Preferred cores consist of metal chalcogenides, preferably metaloxides, or metal pnictides, preferably nitrides or phosphides. Metals inthe sense of these terms are all elements which can occur aselectropositive partner compared with the counterions, such as theclassical metals of the sub-groups, or the main-group metals from thefirst and second main groups, but also all elements from the third maingroup, as well as silicon, germanium, tin, lead, phosphorus, arsenic,antimony and bismuth. The preferred metal chalcogenides and metalpnictides include, in particular, silicon dioxide, aluminium oxide,gallium nitride, boron nitride, aluminium nitride, silicon nitride andphosphorus nitride.

[0055] The starting materials employed for the production of thecore/shell particles according to the invention in a variant of thepresent invention are preferably monodisperse cores of silicon dioxide,which can be obtained, for example, by the process described in U.S.Pat. No. 4,911,903. The cores here are produced by hydrolyticpolycondensation of tetraalkoxysilanes in an aqueous-ammoniacal medium,where firstly a sol of primary particles is produced, and the resultantSiO₂ particles are subsequently converted into the desired particle sizeby continuous, controlled metered addition of tetraalkoxysilane. Thisprocess enables the production of monodisperse SiO₂ cores having meanparticle diameters of between 0.05 and 10 μm with a standard deviationof 5%.

[0056] Also preferred as starting material are SiO₂ cores which havebeen coated with (semi)metals or metal oxides which do not absorb in thevisible region, such as, for example, TiO₂, ZrO₂, ZnO₂, SnO₂ or Al₂O₃.The production of SiO₂ cores coated with metal oxides is described ingreater detail in, for example, U.S. Pat. No. 5,846,310, DE 198 42 134and DE 199 29 109.

[0057] The starting material employed can also be monodisperse cores ofnonabsorbent metal oxides, such as TiO₂, ZrO₂, ZnO₂, SnO₂ or Al₂O₃, ormetal-oxide mixtures. Their production is described, for example, in EP0 644 914. Furthermore, the process of EP 0 216 278 for the productionof monodisperse SiO₂ cores can readily be applied to other oxides withthe same result. Tetraethoxysilane, tetrabutoxytitanium,tetrapropoxyzirconium or mixtures thereof are added in one portion, withvigorous mixing, to a mixture of alcohol, water and ammonia, whosetemperature is set precisely to from 30 to 40° C. using a thermostat,and the resultant mixture is stirred vigorously for a further 20seconds, giving a suspension of monodisperse cores in the nanometreregion. After a post-reaction time of from 1 to 2 hours, the cores areseparated off in a conventional manner, for example by centrifugation,washed and dried.

[0058] Suitable starting materials for the production of the core/shellparticles according to the invention are furthermore also monodispersecores of polymers which contain included particles, for example metaloxides. Materials of this type are available, for example, from microcaps Entwicklungs-und Vertriebs GmbH in Rostock. Microencapsulationsbased on polyesters, polyamides and natural and modified carbohydratesare produced in accordance with customer-specific requirements.

[0059] It is furthermore possible to employ monodisperse cores of metaloxides which have been coated with organic materials, for examplesilanes. The monodisperse cores are dispersed in alcohols and modifiedwith conventional organoalkoxysilanes. The silanisation of sphericaloxide particles is also described in DE 43 16 814. The silanes herepreferably form the above-mentioned interlayer.

[0060] For the intended use of the core/shell particles according to theinvention for the production of mouldings, it is important that theshell material is filmable, i.e. that it can be softened,visco-elastically plasticised or liquefied by simple measures to such anextent that the cores of the core/shell particles are at least able toform domains having a regular arrangement. The regularly arranged coresin the matrix formed by film formation of the shell of the core/shellparticles form a diffraction grating, which causes interferencephenomena and thus results in very interesting colour effects.

[0061] The materials of core and shell may, as long as they satisfy theconditions indicated above, be of an inorganic, organic or even metalliccharacter or they may be hybrid materials.

[0062] In view of the possibility of varying the invention-relevantproperties of the cores of the core/shell particles according to theinvention as needed, however, it is often advantageous for the cores tocomprise one or more polymers and/or copolymers (core polymers) or toconsist of polymers of this type.

[0063] The cores preferably comprise a single polymer or copolymer. Forthe same reason, it is advantageous for the shell of the core/shellparticles according to the invention likewise to comprise one or morepolymers and/or copolymers (shell polymers; matrix polymers) or polymerprecursors and, if desired, auxiliaries and additives, where thecomposition of the shell may be selected in such a way that it isessentially dimensionally stable and tack-free in a non-swellingenvironment at room temperature.

[0064] With the use of polymer substances as shell material and, ifdesired, core material, the person skilled in the art gains the freedomto determine their relevant properties, such as, for example, theircomposition, the particle size, the mechanical data, the refractiveindex, the glass transition temperature, the melting point and thecore:shell weight ratio and thus also the applicational properties ofthe core/shell particles, which ultimately also affect the properties ofthe mouldings produced therefrom.

[0065] Polymers and/or copolymers which may be present in the corematerial or of which it consists are high-molecular-weight compoundswhich conform to the specification given above for the core material.Both polymers and copolymers of polymerisable unsaturated monomers andpolycondensates and copolycondensates of monomers containing at leasttwo reactive groups, such as, for example, high-molecular-weightaliphatic, aliphatic/aromatic or fully aromatic polyesters, polyamides,polycarbonates, polyureas and polyurethanes, but also amino and phenolicresins, such as, for example, melamine-formaldehyde, urea-formaldehydeand phenol-formaldehyde condensates, are suitable.

[0066] For the production of epoxy resins, which are likewise suitableas core material, epoxide prepolymers, which are obtained, for example,by reaction of bisphenol A or other bisphenols, resorcinol,hydroquinone, hexanediol or other aromatic or aliphatic diols orpolyols, or phenol-formaldehyde condensates, or mixtures thereof withone another, with epichlorohydrin or other di- or polyepoxides, areusually mixed with further condensation-capable compounds directly or insolution and allowed to cure.

[0067] The polymers of the core material are advantageously, in apreferred variant of the invention, crosslinked (co)polymers, sincethese usually only exhibit their glass transition at high temperatures.These crosslinked polymers; may either already have been crosslinkedduring the polymerisation or polycondensation or copolymerisation orcopolycondensation or may have been post-crosslinked in a separateprocess step after the actual (co)polymerisation or(co)polycondensation.

[0068] A detailed description of the chemical composition of suitablepolymers follows below.

[0069] In principle, polymers of the classes already mentioned above, ifthey are selected or constructed in such a way that they conform to thespecification given above for the shell polymers, are suitable for theshell material and for the core material.

[0070] For certain applications, such as, for example, for theproduction of coatings or coloured films, it is favourable, as alreadystated above, for the polymer material of the matrix phase-forming shellof the core/shell particles according to the invention to be anelastically deformable polymer, for example a polymer having a low glasstransition temperature. In this case, it is possible to achieve asituation in which the colour of the moulding according to the inventionvaries on elongation and compression. Also of interest for theapplication are core/shell particles according to the invention which,on film formation, result in mouldings which exhibit dichroism.

[0071] Polymers which meet the specifications for a shell material arelikewise present in the groups of polymers and copolymers ofpolymerisable unsaturated monomers and polycondensates andcopolycondensates of monomers containing at least two reactive groups,such as, for example, high-molecular-weight aliphatic,aliphatic/aromatic or fully aromatic polyesters and polyamides.

[0072] Taking into account the above conditions for the properties ofthe shell polymers (=matrix polymers), selected units from all groups oforganic film formers are in principle suitable for their production.

[0073] Some further examples are intended to illustrate the broad rangeof polymers which are suitable for the production of the shells.

[0074] If the shell is intended to have a comparatively low refractiveindex, polymers such as polyethylene, polypropylene, polyethylene oxide,polyacrylates, polymethacrylates, polybutadiene, polymethylmethacrylate, polytetrafluoroethylene, polyoxymethylene, polyesters,polyamides, polyepoxides, polyurethane, rubber, polyacrylonitrile andpolyisoprene, for example, are suitable.

[0075] If the shell is intended to have a comparatively high refractiveindex, polymers having a preferably aromatic basic structure, such aspolystyrene, polystyrene copolymers, such as, for example, SAN,aromatic-aliphatic polyesters and polyamides, aromatic polysulfones andpolyketones, polyvinyl chloride, polyvinylidene chloride and, onsuitable selection of a high-refractive-index core material, alsopolyacrylonitrile or polyurethane, for example, are suitable for theshell.

[0076] In an embodiment of core/shell particles which is particularlypreferred in accordance with the invention, the core consists ofcrosslinked polystyrene and the shell of a polyacrylate, preferablypolyethyl acrylate, polybutyl acrylate, polymethyl methacrylate and/or acopolymer thereof.

[0077] With respect to particle size, particle-size distribution andrefractive-index differences, the above-stated regarding the mouldingsapplies analogously to the core/shell particles according to theinvention.

[0078] With respect to the processability of the core/shell particlesinto mouldings, it is advantageous for the core:shell weight ratio to bein the range from 2:1 to 1:5, preferably in the range from 3:2 to 1:3and particularly preferably in the region below 1.2:1. In specificembodiments of the present invention, it is even preferred for thecore:shell weight ratio to be less than 1:1, a typical upper limit forthe shell content being at a core:shell weight ratio of 2:3.

[0079] The core/shell particles according to the invention can beproduced by various processes. A preferred way of obtaining theparticles is a further subject-matter of the present invention. This isa process for the production of core/shell particles by a) surfacetreatment of monodisperse cores, and b) application of the shell oforganic polymers to the treated cores.

[0080] In a process variant, the monodisperse cores are obtained in stepa) by emulsion polymerisation.

[0081] In a preferred variant of the invention, a crosslinked polymericinterlayer, which preferably contains reactive centres to which theshell can be covalently bonded, is applied to the cores in step a),preferably by emulsion polymerisation or by ATR polymerisation. ATRpolymerisation here stands for atom transfer radical polymerisation, asdescribed, for example, in K. Matjaszewski, Practical Atom TransferRadical Polymerisation, Polym. Mater. Sci. Eng. 2001, 84. Theencapsulation of inorganic materials by means of ATRP is described, forexample, in T. Werne, T. E. Patten, Atom Transfer Radical Polymerisationfrom Nanoparticles: A Tool for the Preparation of Well-Defined HybridNanostructures and for Understanding the Chemistry ofControlled/“Living” Radical Polymerisation from Surfaces, J. Am. Chem.Soc. 2001, 123, 7497-7505 and WO 00/11043. The performance both of thismethod and of emulsion polymerisations is familiar to the person skilledin the art of polymer preparation and is described, for example, in theabove-mentioned literature references.

[0082] The liquid reaction medium in which the polymerisations orcopolymerisations can be carried out consists of the solvents,dispersion media or diluents usually employed in polymerisations, inparticular in emulsion polymerisation processes. The choice here is madein such a way that the emulsifiers employed for homogenisation of thecore particles and shell precursors are able to develop adequateefficacy. Suitable liquid reaction media for carrying out the processaccording to the invention are aqueous media, in particular water.

[0083] Suitable for initiation of the polymerisation are, for example,polymerisation initiators which decompose either thermally orphotochemically, form free radicals and thus initiate thepolymerisation. Preferred thermally activatable polymerisationinitiators here are those which decompose at between 20 and 180° C., inparticular at between 20 and 80° C. Particularly preferredpolymerisation initiators are peroxides, such as dibenzoyl peroxide,di-tertbutyl peroxide, peresters, percarbonates, perketals,hydroperoxides, but also inorganic peroxides, such as H₂O₂, salts ofperoxosulfuric acid and peroxodisulfuric acid, azo compounds, alkylboroncompounds, and hydrocarbons which decompose homolytically. Theinitiators and/or photoinitiators, which, depending on the requirementsof the polymerised material, are employed in amounts of between 0.01 and15% by weight, based on the polymerisable components, can be usedindividually or, in order to utilise advantageous synergistic effects,in combination with one another. In addition, use is made of redoxsystems, such as, for example, salts of peroxodisulfuric acid andperoxosulfuric acid in combination with low-valency sulfur compounds,particularly ammonium peroxodisulfate in combination with sodiumdithionite.

[0084] Corresponding processes have also been described for theproduction of polycondensation products. Thus, it is possible for thestarting materials for the production of polycondensation products to bedispersed in inert liquids and condensed, preferably with removal oflow-molecular-weight reaction products, such as water or—for example onuse of di(lower alkyl) dicarboxylates for the preparation of polyestersor polyamides—lower alkanols.

[0085] Polyaddition products are obtained analogously by reaction ofcompounds which contain at least two, preferably three, reactive groups,such as, for example, epoxide, cyanate, isocyanate or isothiocyanategroups, with compounds carrying complementary reactive groups. Thus,isocyanates react, for example, with alcohols to give urethanes, withamines to give urea derivatives, while epoxides react with thesecomplementary groups to give hydroxyethers or hydroxyamines. Like thepolycondensations, polyaddition reactions can also advantageously becarried out in an inert solvent or dispersion medium.

[0086] It is also possible for aromatic, aliphatic or mixedaromatic/aliphatic polymers, for example polyesters, polyurethanes,polyamides, polyureas, polyepoxides or also solution polymers, to bedispersed or emulsified (secondary dispersion) in a dispersion medium,such as, for example, in water, alcohols, tetrahydrofuran orhydrocarbons, and to be post-condensed, crosslinked and cured in thisfine distribution.

[0087] The stable dispersions required for these polymerisation,polycondensation or polyaddition processes are generally produced usingdispersion auxiliaries.

[0088] The dispersion auxiliaries used are preferably water-soluble,high-molecular-weight organic compounds having polar groups, such aspolyvinylpyrrolidone, copolymers of vinyl propionate or acetate andvinylpyrrolidone, partially saponified copolymers of an acrylate andacrylonitrile, polyvinyl alcohols having different residual acetatecontents, cellulose ethers, gelatin, block copolymers, modified starch,low-molecular-weight polymers containing carboxyl and/or sulfonylgroups, or mixtures of these substances.

[0089] Particularly preferred protective colloids are polyvinyl alcoholshaving a residual acetate content of less than 35 mol %, in particularfrom 5 to 39 mol %, and/or vinylpyrrolidone-vinyl propionate copolymershaving a vinyl ester content of less than 35% by weight, in particularfrom 5 to 30% by weight.

[0090] It is possible to use nonionic or ionic emulsifiers, if desiredalso as a mixture. Preferred emulsifiers are optionally ethoxylated orpropoxylated, relatively long-chain alkanols or alkylphenols havingdifferent degrees of ethoxylation or propoxylation (for example adductswith from 0 to 50 mol of alkylene oxide) or neutralised, sulfated,sulfonated or phosphated derivatives thereof. Neutraliseddialkylsulfosuccinic acid esters or alkyldiphenyl oxide disulfonates arealso particularly suitable.

[0091] Particularly advantageous are combinations of these emulsifierswith the above-mentioned protective colloids, since particularly finelydivided dispersions are obtained therewith.

[0092] Special processes for the production of monodisperse polymerparticles have also already been described in the literature (forexample R. C. Backus, R. C. Williams, J. Appl. Physics 19, p. 1186(1948)) and can advantageously be employed, in particular, for theproduction of the cores. It need merely be ensured here that theabove-mentioned particle sizes are observed. A further aim is thegreatest possible uniformity of the polymers. The particle size inparticular can be set via the choice of suitable emulsifiers and/orprotective colloids or corresponding amounts of these compounds.

[0093] Through the setting of the reaction conditions, such astemperature, pressure, reaction duration and use of suitable catalystsystems, which influence the degree of polymerisation in a known manner,and the choice of the monomers employed for their production—in terms oftype and proportion—the desired property combinations of the requisitepolymers can be set specifically. The particle size here can be set, forexample, through the choice and amount of the initiators and otherparameters, such as the reaction temperature. The corresponding settingof these parameters does not present any difficulties at all to theperson skilled in the art in the area of polymerisation.

[0094] Monomers which result in polymers having a high refractive indexare generally those which contain aromatic moieties or those whichcontain heteroatoms having a high atomic number, such as, for example,those halogen atoms, in particular bromine or iodine atoms, sulfur ormetal ions, i.e. atoms or atomic groups which increase thepolarisability of the polymers.

[0095] Polymers having a low refractive index are accordingly obtainedfrom monomers or monomer mixtures which do not contain the said moietiesand/or atoms of high atomic number or only do so in a small proportion.

[0096] A review of the refractive indices of various common homopolymersis given, for example, in Ullmanns Encyklopädie der technischen Chemie[Ullmann's Encyclopaedia of Industrial Chemistry], 5th Edition, VolumeA21, page 169. Examples of monomers which can be polymerised by means offree radicals and result in polymers having a high refractive index are:

[0097] Group a): styrene, styrenes which are alkyl-substituted on thephenyl ring, α-methylstyrene, mono- and dichlorostyrene,vinylnaphthalene, isopropenyinaphthalene, isopropenylbiphenyl,vinylpyridine, isopropenylpyridine, vinylcarbazole, vinylanthracene,N-benzylmethacrylamide and p-hydroxymethacrylanilide.

[0098] Group b): acrylates containing aromatic side chains, such as, forexample, phenyl (meth)acrylate (=abbreviated notation for the twocompounds phenyl acrylate and phenyl methacrylate), phenyl vinyl ether,benzyl (meth)acrylate, benzyl vinyl ether, and compounds of theformulae:

[0099] In order to improve clarity and simplify the notation of carbonchains in the formulae above and below, only the bonds between thecarbon atoms are shown. This notation corresponds to the depiction ofaromatic cyclic compounds, where, for example, benzene is depicted by ahexagon with alternating single and double bonds.

[0100] Also suitable are compounds containing sulfur bridges instead ofoxygen bridges, such as, for example:

[0101] In the above formulae, R is hydrogen or methyl. The phenyl ringsin these monomers may carry further substituents. Such substituents aresuitable for modifying the properties of the polymers produced fromthese monomers within certain limits. They can therefore be used in atargeted manner to optimise, in particular, the applicationally relevantproperties of the mouldings according to the invention.

[0102] Suitable substituents are, in particular, halogen, NO₂, alkylgroups having from one to twenty carbon atoms, preferably methyl,alkoxides having from one to twenty carbon atoms, carboxyalkyl groupshaving from one to twenty carbon atoms, carbonylalkyl groups having fromone to twenty carbon atoms or —OCOO-alkyl groups having from one totwenty carbon atoms. The alkyl chains in these radicals may themselvesoptionally be substituted or interrupted by divalent heteroatoms orgroups, such as, for example, —O—, —S—, —NH—, —COO—, —OCO— or —OCOO—, innon-adjacent positions.

[0103] Group c): monomers containing heteroatoms, such as, for example,vinyl chloride, acrylonitrile, methacrylonitrile, acrylic acid,methacrylic acid, acrylamide and methacrylamide, or organometalliccompounds, such as, for example,

[0104] Group d): an increase in the refractive index of the polymers isalso achieved by copolymerisation of carboxyl-containing monomers andconversion of the resultant “acidic” polymers into the correspondingsalts with metals of relatively high atomic weight, such as, forexample, preferably with K, Ca, Sr, Ba, Zn, Pb, Fe, Ni, Co, Cr, Cu, Mn,Sn or Cd.

[0105] The above-mentioned monomers, which make a considerablecontribution towards the refractive index of the polymers producedtherefrom, can be homopolymerised or copolymerised with one another.They can also be copolymerised with a certain proportion of monomerswhich make a lesser contribution towards the refractive index. Suchcopolymerisable monomers having a lower refractive index contributionare, for example, acrylates, methacrylates, vinyl ethers or vinyl esterscontaining purely aliphatic radicals.

[0106] In addition, crosslinking agents which can be employed for theproduction of crosslinked polymer cores from polymers produced by meansof free radicals are also all bifunctional or polyfunctional compoundswhich are copolymerisable with the above-mentioned monomers or which cansubsequently react with the polymers with crosslinking.

[0107] Examples of suitable crosslinking agents are presented below,divided into groups for systematisation:

[0108] Group 1: bisacrylates, bismethacrylates and bisvinyl ethers ofaromatic or aliphatic di- or polyhydroxyl compounds, in particular ofbutanediol (butanediol di(meth)acrylate, butanediol bisvinyl ether),hexanediol (hexanediol di(meth)acrylate, hexanediol bisvinyl ether),pentaerythritol, hydroquinone, bishydroxyphenylmethane, bishydroxyphenylether, bishydroxymethylbenzene, bisphenol A or with ethylene oxidespacers, propylene oxide spacers or mixed ethylene oxide/propylene oxidespacers.

[0109] Further crosslinking agents from this group are, for example, di-or polyvinyl compounds, such as divinylbenzene, ormethylenebisacrylamide, triallyl cyanurate, divinylethyleneurea,trimethylolpropane tri(meth)acrylate, trimethylolpropane trivinyl ether,pentaerythritol tetra(meth)acrylate, pentaerythritol tetravinyl ether,and crosslinking agents having two or more different reactive ends, suchas, for example, (meth)allyl (meth)acrylates of the formulae:

[0110] (in which R is hydrogen or methyl).

[0111] Group 2: reactive crosslinking agents which act in a crosslinkingmanner, but in most cases in a post-crosslinking manner, for exampleduring warming or drying, and which are copolymerised into the core orshell polymers as copolymers.

[0112] Examples thereof are: N-methylol(meth)acrylamide,acrylamidoglycolic acid, and ethers and/or esters thereof with C₁- toC₆-alcohols, diacetoneacrylamide (DMM), glycidyl methacrylate (GMA),methacryloyloxypropyltrimethoxysilane (MEMO), vinyltrimethoxysilane andm-isopropenylbenzyl isocyanate (TMI).

[0113] Group 3: carboxyl groups which have been incorporated into thepolymer by copolymerisation of unsaturated carboxylic acids arecrosslinked in a bridge-like manner via polyvalent metal ions. Theunsaturated carboxylic acids employed for this purpose are preferablyacrylic acid, methacrylic acid, maleic anhydride, itaconic acid andfumaric acid. Suitable metal ions are Mg, Ca, Sr, Ba, Zn, Pb, Fe, Ni,Co, Cr, Cu, Mn, Sn and Cd. Particular preference is given to Ca, Mg andZn, Ti and Zr. In addition, monovalent metal ions, such as, for example,Na or K, are also suitable.

[0114] Group 4: post-crosslinked additives, which are taken to mean bis-or polyfunctionalised additives which react irreversibly with thepolymer (by addition or preferably condensation reactions) withformation of a network. Examples thereof are compounds which contain atleast two of the following reactive groups per molecule: epoxide,aziridine, isocyanate, acid chloride, carbodiimide or carbonyl groups,furthermore, for example, 3,4-dihydroxyimidazolinone and derivativesthereof (®Fixapret products from BASF).

[0115] As already explained above, post-crosslinking agents containingreactive groups, such as, for example, epoxide and isocyanate groups,require complementary reactive groups in the polymer to be crosslinked.Thus, isocyanates react, for example, with alcohols to give urethanes,with amines to give urea derivatives, while epoxides react with thesecomplementary groups to give hydroxyethers and hydroxyaminesrespectively.

[0116] The term post-crosslinking is also taken to mean photochemicalcuring or oxidative or air- or moisture-induced curing of the systems.

[0117] The above-mentioned monomers and crosslinking agents can becombined and (co)polymerised with one another as desired and in atargeted manner in such a way that an optionally crosslinked (co)polymerhaving the desired refractive index and the requisite stability criteriaand mechanical properties is obtained.

[0118] It is also possible additionally to copolymerise further commonmonomers, for example acrylates, methacrylates, vinyl esters, butadiene,ethylene or styrene, in order, for example, to set the glass transitiontemperature or the mechanical properties of the core and/or shellpolymers as needed.

[0119] It is likewise preferred in accordance with the invention for theapplication of the shell of organic polymers to be carried out bygrafting, preferably by emulsion polymerisation or ATR polymerisation.The methods and monomers described above can be employed correspondinglyhere.

[0120] In particular on use of inorganic cores, it may also be preferredfor the core to be subjected to a pre-treatment which enables binding ofthe shell before the shell is polymerised on. This can usually consistin chemical functionalisation of the particle surface, as is known fromthe literature for a very wide variety of inorganic materials. It mayparticularly preferably involve application to the surface of chemicalfunctions which, as reactive chain end, enable grafting-on of the shellpolymers. Examples which may be mentioned in particular here areterminal double bonds, epoxy functions and polycondensable groups. Thefunctionalisation of hydroxyl-carrying surfaces with polymers isdisclosed, for example, in EP-A-337 144. Further methods for themodification of particle surfaces are well known to the person skilledin the art and are described, for example, in various textbooks, such asUnger, K. K., Porous Silica, Elsevier Scientific Publishing Company(1979).

[0121] The invention furthermore relates to the use of mouldingsaccording to the invention or of core/shell particles according to theinvention for the production of pigments. The pigments obtainable inthis way are particularly suitable for use in paints, surface coatings,printing inks, plastics, ceramics, glasses and cosmetic formulations.For this purpose, they can also be employed mixed with commerciallyavailable pigments, for example inorganic and organic absorptionpigments, metal-effect pigments and LC pigments. The particles accordingto the invention are furthermore also suitable for the production ofpigment preparations and for the production of dry preparations, suchas, for example, granules. Pigment particles of this type preferablyhave a platelet-shaped structure with an average particle size of 5 μm-5mm.

[0122] The pigments can be produced, for example, by firstly producing afilm from the core/shell particles, which may optionally be cured. Thefilm can subsequently be comminuted in a suitable manner by cutting orcrushing and, if desired, subsequent grinding to give pigments ofsuitable size. This operation can be carried out, for example, in acontinuous belt process.

[0123] The pigment according to the invention can then be used for thepigmentation of surface coatings, powder coatings, paints, printinginks, plastics and cosmetic formulations, such as, for example, oflipsticks, nail varnishes, cosmetic sticks, compact powders, make-ups,shampoos and loose powders and gels.

[0124] The concentration of the pigment in the application system to bepigmented is generally between 0.1 and 70% by weight, preferably between0.1 and 50% by weight and in particular between 1.0 and 20% by weight,based on the total solids content of the system. It is generallydependent on the specific application. Plastics usually comprise thepigment according to the invention in amounts of from 0.01 to 50% byweight, preferably from 0.01 to 25% by weight, in particular from 0.1 to7% by weight, based on the plastic composition. In the coatings area,the pigment mixture is employed in amounts of from 0.1 to 30% by weight,preferably from 1 to 10% by weight, based on the coating dispersion. Inthe pigmentation of binder systems, for example for paints and printinginks for gravure printing, offset printing or screen printing, or asprecursor for printing inks, for example in the form of highly pigmentedpastes, granules, pellets, etc., pigment mixtures with sphericalcolorants, such as, for example, TiO₂, carbon black, chromium oxide,iron oxide, and organic “coloured pigments”, have proven particularlysuitable. The pigment is generally incorporated into the printing ink inamounts of 2-35% by weight, preferably 5-25% by weight and in particular8-20% by weight. Offset printing inks can comprise the pigment inamounts of up to 40% by weight or more. The precursors for printinginks, for example in the form of granules, as pellets, briquettes, etc.,comprise up to 95% by weight of the pigment according to the inventionin addition to the binder and additives. The invention thus also relatesto formulations which comprise the pigment according to the invention.

[0125] The following examples are intended to explain the invention ingreater detail without limiting it.

EXAMPLES

[0126] Abbreviations used:

[0127] BDDA butane-1,4-diol diacrylate

[0128] SDS dodecyl sulfate sodium salt

[0129] SDTH sodium dithionite

[0130] APS ammonium peroxodisulfate

[0131] KOH potassium hydroxide

[0132] ALMA allyl methacrylate

[0133] MMA methyl methacrylate

[0134] EA ethyl acrylate

Example 1 Production of Core/Shell Particles

[0135] A mixture, held at 4° C., consisting of 217 g of water, 0.4 g ofbutanediol diacrylate (Merck, destabilised), 3.6 g of styrene (BASF,destabilised) and 80 mg of sodium dodecylsulfate (SDS; Merck) isintroduced into a stirred reactor, pre-heated to 75° C., fitted withpropeller stirrer, argon protective-gas inlet and reflux condenser, anddispersed with vigorous stirring. Directly after the introduction, thereaction is initiated by direct successive addition of 50 mg of sodiumdithionite (Merck), 250 mg of ammonium peroxodisulfate (Merck) and afurther 50 mg of sodium dithionite (Merck), in each case dissolved in 5g of water. After 10 minutes, a monomer emulsion comprising 6.6 g ofbutanediol diacrylate (Merck, destabilised), 59.4 g of styrene (BASF,destabilised), 0.3 g of SDS, 0.1 g of KOH and 90 g of water is meteredin continuously over a period of 210 minutes. The reactor contents arestirred for 30 minutes without further addition. A second monomeremulsion comprising 3 g of allyl methacrylate (Merck, destabilised), 27g of methyl methacrylate (BASF, destabilised), 0.15 g of SDS (Merck) and40 g of water is subsequently metered in continuously over a period of90 minutes. The reactor contents are subsequently stirred for 30 minuteswithout further addition. A monomer emulsion comprising 130 g of ethylacrylate (BASF, destabilised), 139 g of water and 0.33 g of SDS (Merck)is subsequently metered in continuously over a period of 180 minutes.The mixture is subsequently stirred for a further 60 minutes forvirtually complete reaction of the monomers. The core/shell particlesare subsequently precipitated in 1 l of methanold, 1 l of distilledwater is added, and the particles are filtered off with suction anddried.

[0136] Scanning and transmission electron photomicrographs of thecore/shell particles show that the particles have a particle size of 220nm.

[0137] While carrying out the experiment analogously, the particle sizeof the particles can be varied via the surfactant concentration in theinitially introduced mixture. Selection of corresponding amounts ofsurfactant gives the following particle sizes: Amount of surfactant [mgof SDS] Particle size [nm] 80 220 90 200 100 180 110 160

Example 2 Production of Granules of the Core/Shell Particles

[0138] 3 kg of the core/shell particles from Example 1 are comminuted ina cutting mill (Rapid, model 1528) with ice cooling and subsequentlycompounded in a single-screw extruder (Plasti-Corder; Brabender; screwdiameter 19 mm with 1-hold die (3 mm)). After a cooling zone, theextrudate is granulated in an A 90-5 granulator (Automatik).

Example 3a Production of a Film from Core/Shell Particles

[0139] 2 g of the granules from Example 2 are heated to a temperature of120° C. without pressure in a Collin 300P press and pressed at apressure of 30 bar to give a film. After cooling to room temperature,the pressure is reduced again.

[0140] Transmission electron photomicrographs (FIGS. 1 and 2 showparticles having a size of 180 nm) confirm the alignment of the cores inthe shell matrix to give an extended crystal lattice. FIG. 2 shows theorientation of the three layers of core/shell particles one on top ofthe other to give an fcc lattice.

[0141] The results of optical absorption spectroscopy (UV/VIS) are shownin FIG. 4 and FIG. 5.

Example 3b Production of a Film from Core/Shell Particles

[0142] 25 g of the granules from Example 2 are heated to a temperatureof 150° C. without pressure in a press with cartridge cooling system(Dr. Collin GmbH; model 300E) and pressed at a pressure of 250 bar togive a film. After cooling to room temperature, the pressure is reducedagain after 8 minutes.

Example 4 Production of Mouldings by Injection Moulding

[0143] 0.2% by weight of release agent (Ceridust® 3615; Clariant) isadmixed with the granules from Example 2. The mixture is processedfurther using a Klöckner Ferromatik 75 FX 75-2F injection-mouldingmachine. The granules are injected at 900 bar at a barrel temperature of190° C. into the mould held at 80° C., subsequently cooled in the mouldand demoulded at a mould temperature of 30° C. This gives mouldingshaving an optical effect which is dependent on the viewing angle.

Example 5 Production of a Flat Film (Tape)

[0144] Granules from Example 2 are processed in a flat-film machineconsisting of a single-screw extruder (Göttfert; model Extrusiometer;screw diameter 20 mm; L/D 25), a thickness-adjustable film die (width135 mm) and a heatable polishing stack (Leistritz; roll diameter 15 mm;roll width 350 mm). A film tape with a width of 125 mm and a thicknessof 1 mm is obtained.

Example 6 Production of Core/Shell Particles Having a Silicon DioxideCore (150 nm)

[0145] 66 g of Monospher® 150 suspension (Merck; solids content 38% byweight, corresponding to 25 g of SiO₂ monospheres; average particle size150 nm; standard deviation of the average particle size <5%) areintroduced with 354 g of water into a stirred twin-wall reactor, held at25° C., fitted with argon protective-gas inlet, reflux condenser andpropeller stirrer, a solution of 450 mg of aluminium trichloridehexahydrate (Acros) in 50 ml is added, and the mixture is stirredvigorously for 30 minutes. A solution of 40 mg of sodium dodecylsulfatein 50 g of water is subsequently added, and the mixture is stirredvigorously for a further 30 minutes.

[0146] 50 mg of sodium dithionite, 150 mg of ammonium peroxodisulfateand a further 50 mg of sodium dithionite, in each case in 5 g of water,are then added directly one after the other. Immediately after theaddition, the reactor is heated to 75° C., and 25 g of ethyl acrylateare metered in continuously over a period of 120 minutes. The reactorcontents are subsequently stirred at 75° C. for a further 60 minutes forcomplete reaction of the monomer.

[0147] The resultant hybrid material is filtered off and dried andprocessed further as described in Examples 2 to 5.

Example 6a

[0148] Core/shell particles having different silicon dioxide corediameters (for example 100 nm) can be produced analogously.

Example 7 Production of Core/Shell Particles Having a Silicon DioxideCore (250 nm)

[0149] 60 g of Monospher® 250 (Merck; average particle size 250 nm;standard deviation of the average particle size <5%) are suspended inethanol. 6 g of 3-methacryloxypropyltrimethoxysilane are added dropwiseat 75° C. over the course of 15 minutes with vigorous stirring. After 12hours at 75° C., the resultant powder is separated off and dried.

[0150] 90 g of water and 50 mg of sodium dodecylsulfate are added to 10g of the functionalised Monospher® 250, and the mixture is stirredvigorously for 1 day for dispersal. The suspension is subsequentlydispersed in a homogeniser (Niro Soavi, NS1001L). 70 g of water areadded to the dispersion, and the mixture is cooled to 4° C.

[0151] The dispersion is subsequently introduced into a stirredtwin-wall reactor fitted with argon protective-gas inlet, refluxcondenser and propeller stirrer. 50 mg of sodium dithionite, 150 mg ofammonium peroxodisulfate and a further 50 mg of sodium dithionite, ineach case in 5 g of water, are then added directly one after the other.Immediately after the addition, the reactor is heated to 75° C., and anemulsion of 10 g of ethyl acrylate and 20 g of water is metered incontinuously over a period of 120 minutes. The reactor contents aresubsequently stirred at 75° C. for a further 60 minutes for completereaction of the monomer.

[0152] The resultant hybrid material is precipitated in a solution of 10g of calcium chloride and 500 g, of water, filtered off and dried andprocessed further as described in Examples 2 to 5.

Example 8 Production of Core/Shell Particles in which the Core is BuiltUp from Silicon Dioxide with an Outer Sheath of Titanium Dioxide

[0153] 80 g of Monospher®100 (monodisperse silicon dioxide beads havinga mean size of 100 nm with a standard deviation of <5%) from Merck KGaAare dispersed in 800 ml of ethanol at 40° C. A freshly prepared solutionconsisting of 50 g of tetraethyl orthotitanate (Merck KGaA) and 810 mlof ethanol is metered into the Monospher/ethanol dispersion togetherwith deionised water with vigorous stirring. The metering is initiallycarried out over a period of 5 minutes at a dropwise addition rate of0.03 ml/min (titanate solution) or 0.72 ml/min. The titanate solution isthen added at 0.7 ml/min and the water at 0.03 ml/min until thecorresponding containers are completely empty. For further processing,the ethanolic dispersion is stirred under reflux at 70° C. with cooling,and 2 g of methacryloxypropyltrimethoxysilane (ABCR), dissolved in 10 mlof ethanol, are added over a period of 15 minutes. After the mixture hasbeen refluxed overnight, the resultant powder is separated off anddried. 90 g of water and 50 mg of sodium dodecylsulfate are added to 10g of the functionalised silicon dioxide/titanium dioxide hybridparticles, and the mixture is stirred vigorously for 1 day fordispersal. The suspension is subsequently dispersed in a homogeniser(Niro Soavi, NS1001L). 70 g of water are added to the dispersion, andthe mixture is cooled to 4° C.

[0154] The dispersion is subsequently introduced into a stirredtwin-wall reactor with argon protective-gas inlet, reflux condenser andpropeller stirrer. 50 mg of sodium dithionite, 150 mg of ammoniumperoxodisulfate and a further 50 mg of sodium dithionite, in each casein 5 g of water, are then added directly one after the other.Immediately after the addition, the reactor is heated to 75° C., and anemulsion of 10 g of ethyl acrylate and 20 g of water is metered incontinuously over a period of 120 minutes. The reactor contents aresubsequently stirred at 75° C. for a further 60 minutes for completereaction of the monomer.

[0155] The resultant hybrid material is precipitated in a solution of 10g of calcium chloride and 500 g of water, filtered off and dried andprocessed further as described in Examples 2 to 5.

Example 9 Production of Core/Shell Particles in a 5 l Reactor

[0156] A mixture, held at 4° C., consisting of 1519 g of deionisedwater, 2.8 g of BDDA, 25.2 g of styrene and 1030 mg of SDS is introducedinto a 5 l jacketed reactor, heated to 75° C., fitted withdouble-propeller stirrer, argon protective-gas inlet and refluxcondenser, and dispersed with vigorous stirring. The reaction isimmediately initiated by successive injection of 350 mg of SDTH, 1.75 gof APS and a further 350 mg of SDTH, in each case dissolved in about 20ml of water. The injection is carried out by means of disposablesyringes. After 20 minutes, a monomer emulsion comprising 56.7 g ofBDDA, 510.3 g of styrene, 2.625 g of SDS, 0.7 g of KOH and 770 g ofwater is metered in continuously over a period of 120 minutes via arotary piston pump. The reactor contents are stirred for 30 minuteswithout further addition. A second monomer emulsion comprising 10.5 g ofALMA, 94.50 g of methyl methacrylate, 0.525 g of SDS and 140 g of wateris subsequently metered in continuously over a period of 30 minutes viathe rotary piston pump. After about 15 minutes, 350 mg of APS are added,and the mixture is then stirred for a further 15 minutes. A thirdmonomer emulsion comprising 900 g of EA, 2.475 g of SDS and 900 g ofwater is then metered in continuously over a period of 240 minutes viathe rotary piston pump. The mixture is subsequently stirred for afurther 120 minutes. Before and after each initially introduced mixturechange, argon is passed in for about half a minute. Next day, thereactor is heated to 95° C., and a steam distillation is carried out.The core/shell particles are subsequently precipitated in 4 l ofethanol, washed with 5% calcium chloride solution, filtered off anddried and processed further as described in Examples 2 to 5. Mouldingshaving a colour effect (colour flop) in the red-green region areobtained.

Example 10 Production of Core/Shell Particles Having a Butyl AcrylateShell

[0157] A mixture, held at 4° C., consisting of 217 g of water, 0.4 g ofbutanediol diacrylate (Merck, destabilised), 3.6 g of styrene (BASF,destabilised) and 80 mg of sodium dodecylsulfate (SDS; Merck) isintroduced into a stirred reactor, pre-heated to 75° C., fitted withpropeller stirrer, argon protective-gas inlet and reflux condenser, anddispersed with vigorous stirring. Immediately after the introduction,the reaction is initiated by direct successive addition of 50 mg ofsodium dithionite (Merck), 250 mg of ammonium peroxodisulfate (Merck)and a further 50 mg of sodium dithionite (Merck), in each case dissolvedin 5 g of water. After 10 minutes, a monomer emulsion comprising 6.6 gof butanediol diacrylate (Merck, destabilised), 59.4 g of styrene (BASF,destabilised), 0.3 g of SDS, 0.1 g of KOH and 90 g of water is meteredin continuously over a period of 210 minutes. The reactor contents arestirred for 30 minutes without further addition. A second monomeremulsion comprising 3 g of allyl methacrylate (Merck, destabilised), 27g of methyl methacrylate (BASF, destabilised), 0.15 g of SDS (Merck) and40 g of water is subsequently metered in continuously over a period of90 minutes. The reactor contents are subsequently stirred for 30 minuteswithout further addition. A monomer emulsion comprising 130 g of butylacrylate (Merck, destabilised), 139 g of water and 0.33 g of SDS (Merck)is subsequently metered in continuously over a period of 180 minutes.The mixture is subsequently stirred for a further 60 minutes forvirtually complete reaction of the monomers. The core/shell particlesare subsequently precipitated in 1 l of methanol, 1 l of distilled wateris added, and the particles are filtered off with suction, dried andprocessed further as described in Examples 2 to 5.

Example 11 Production of Core/Shell Particles Having an EthylAcrylate/butyl Acrylate Shell

[0158] A mixture, held at 4° C., consisting of 217 g of water, 0.4 g ofbutanediol diacrylate (Merck, destabilised), 3.6 g of styrene (BASF,destabilised) and 60 mg of sodium dodecylsulfate (SDS; Merck) isintroduced into a stirred reactor, pre-heated to 75° C., fitted withpropeller stirrer, argon protective-gas inlet and reflux condenser, anddispersed with vigorous stirring. Immediately after the introduction,the reaction is initiated by direct successive addition of 50 mg ofsodium dithionite (Merck), 300 mg of ammonium peroxodisulfate (Merck)and a further 50 mg of sodium dithionite (Merck), in each case dissolvedin 5 g of water. After 10 minutes, a monomer emulsion comprising 8.1 gof butanediol diacrylate (Merck, destabilised), 72.9 g of styrene (BASF,destabilised), 0.375 g of SDS, 0.1 g of KOH and 110 g of water ismetered in continuously over a period of 150 minutes. The reactorcontents are stirred for 30 minutes without further addition. A secondmonomer emulsion comprising 1.5 g of allyl methacrylate (Merck,destabilised), 13.5 g of methyl methacrylate (BASF, destabilised), 0.075g of SDS (Merck) and 20 g of water is subsequently metered incontinuously over a period of 45 minutes. The reactor contents aresubsequently stirred for 30 minutes without further addition. 50 mg ofAPS dissolved in 5 g of water are subsequently added. A monomer emulsioncomprising 59.4 g of ethyl acrylate (Merck, destabilised), 59.4 g ofbutyl acrylate, 1.2 g of acrylic acid, 120 g of water and 0.33 g of SDS(Merck) is subsequently metered in continuously over a period of 240minutes. The mixture is subsequently stirred for a further 60 minutesfor virtually complete reaction of the monomers. The core/shellparticles are subsequently precipitated in 1 l of methanol, 1 l ofdistilled water is added, and the particles are filtered off withsuction and dried and processed further as described in Examples 2 to 5.

FIGURES

[0159]FIG. 1: Transmission electron photomicrograph of a section througha film with a thickness of 1 mm produced as described in Example 3a(particle size 180 nm).

[0160]FIG. 2: Transmission electron photomicrograph of the plan view ofa film produced as described in Example 3a (particle size 180 nm). Threelayers of core/shell particles one on top of the other can be seen.

[0161]FIG. 3: Model of the crystallisation mechanism; rubber elasticityof the shell.

[0162]FIG. 4: Absorption spectra of various films comprising core/shellparticles (as described in Example 3a);

[0163] a: average particle separation [nm]

[0164]FIG. 5: Absorption spectra of a film comprising core/shellparticles (as described in Example 3a; average particle separation=200nm) as a function of the angle θ between the film surface and theincident light beam.

1. Moulding having an optical effect, essentially consisting ofcore/shell particles whose shell forms a matrix and whose core isessentially solid and has an essentially monodisperse size distribution,where a difference exists between the refractive indices of the corematerial and of the shell material, characterised in that the mouldingis obtainable by a process in which a) the core/shell particles areheated to a temperature at which the shell is flowable, and b) theflowable core/shell particles from a) are subjected to the action of amechanical force.
 2. Moulding according to claim 1, characterised inthat, in the core/shell particles, the shell is bonded to the core viaan interlayer.
 3. Moulding according to claim 1, characterised in thatthe core consists of a material which is either not flowable or becomesflowable at a temperature above the melting point of the shell material.4. Moulding according to claim 1, characterised in that the moulding isobtainable by a process in which the temperature in step a) is at least40° C., preferably at least 60° C., above the glass transitiontemperature of the shell.
 5. Moulding according to claim 1,characterised in that the moulding is obtainable by a process in whichc) the core/shell particles are cooled under the action of themechanical force from b) to a temperature at which the shell is nolonger flowable.
 6. Moulding according to claim 1, characterised in thatthe action of mechanical force takes place through uniaxial pressing,and the moulding is preferably a film.
 7. Moulding according to claim 1,characterised in that the action of mechanical force takes place duringan injection-moulding operation.
 8. Moulding according to claim 7,characterised in that the injection mould has a large cooling-channelcross section.
 9. Moulding according to claim 1, characterised in thatthe action of mechanical force takes place during extrusion. 10.Moulding according to claim 1, characterised in that the mouldingconsists of at least 60% by weight, preferably at least 80% by weightand particularly preferably at least 95% by weight, of core/shellparticles.
 11. Moulding according to claim 1, characterised in that thecore/shell particles have a mean particle diameter in the range fromabout 5 nm to about 2000 nm, preferably in the range from about 5 to 20nm or in the range 50-500 nm.
 12. Moulding according to claim 1,characterised in that the difference between the refractive indices ofthe core material and of the shell material is at least 0.001,preferably at least 0.01 and particularly preferably at least 0.1. 13.Moulding according to claim 1, characterised in that furthernanoparticles, preferably inorganic nanoparticles, particularlypreferably nanoparticles of metals, such as gold, or of II-VI or III-Vsemiconductors, such as zinc sulfide or gallium arsenide, are includedin the matrix phase in addition to the cores, nanoparticles of metals ofII-VI or III-V semiconductors or of materials which influence themagnetic/electrical (electronic) properties of the materials, preferrednanoparticles being, in particular, those selected from noble metals,such as silver, gold and platinum, semiconductors or insulators, such aszinc chalcogenides and cadmium chalcogenides, oxides, such as haematite,magnetite or perovskite, or metal pnictides, for example galliumnitride, or mixed phases of these materials
 14. Core/shell particleswhose core is essentially solid and has an essentially monodisperse sizedistribution, where a difference exists between the refractive indicesof the core material and of the shell material, characterised in thatthe core consists of a material which is either not flowable or becomesflowable at a temperature above the melting point of the shell material,and the shell is bonded to the core via an interlayer.
 15. Core/shellparticles according to claim 14, characterised in that the shellconsists of essentially uncrosslinked organic polymers, which arepreferably grafted onto the core via an at least partially crosslinkedinterlayer.
 16. Core/shell particles according to claim 14,characterised in that the core consists of an organic polymer, which ispreferably crosslinked.
 17. Core/shell particles according to claim 14,characterised in that the core consists of an inorganic material,preferably a metal or semimetal or a metal chalcogenide or metalpnictide, particularly preferably silicon dioxide.
 18. Core/shellparticles according to claim 14, characterised in that the particleshave a mean particle diameter in the range from about 5 nm to about 2000nm, preferably in the range from about 5 to 20 nm or in the range100-500 nm.
 19. Core/shell particles according to claim 14,characterised in that the core:shell weight ratio is in the range from2:1 to 1:5, preferably in the range from 3:2 to 1:3 and particularlypreferably in the region below 1.2:1.
 20. Core/shell particles accordingto claim 14, characterised in that the core consists of crosslinkedpolystyrene, and the shell consists of a polyacrylate, preferablypolyethyl acrylate, polybutyl acrylate, polymethyl methacrylate and/or acopolymer thereof.
 21. Use of core/shell particles according to claim 14for the production of mouldings.
 22. Process for the production ofmouldings having an optical effect, characterised in that a) core/shellparticles whose shell forms a matrix and whose core is essentially solidand has an essentially monodisperse size distribution, where adifference exists between the refractive indices of the core materialand of the shell material, are heated to a temperature at which theshell is flowable, and b) the flowable core/shell particles from a) aresubjected to a mechanical force.
 23. Process for the production ofmouldings according to claim 22, characterised in that in a step c) thecore/shell particles are cooled under the action of the shear force fromb) to a temperature at which the shell is no longer flowable. 24.Process for the production of mouldings according to claim 22,characterised in that the action of mechanical force takes place duringan injection-moulding operation, and the injection mould preferably hasa large cooling-channel cross section.
 25. Process for the production ofcore/shell particles by a) surface treatment of monodisperse cores, b)application of the shell of organic polymers to the treated cores froma).
 26. Process for the production of core/shell particles according toclaim 25, characterised in that the monodisperse cores are obtained in astep a1) by emulsion polymerisation, and a crosslinked polymericinterlayer, which preferably contains reactive centres to which theshell can be covalently bonded, is applied to the cores in a step a2),preferably by emulsion polymerisation or by ATR polymerisation. 27.Process for the production of core/shell particles according to claim25, characterised in that step b) involves grafting, preferably byemulsion polymerisation or ATR polymerisation.
 28. Process for theproduction of core/shell particles according to claim 25, characterisedin that the inorganic core is subjected to a pretreatment which enablesbinding of the shell before the shell is polymerised on.
 29. Use ofmouldings according to claim 1 for the production of pigments.
 30. Usecore/shell particles according to claim 14 for the production ofpigments.